/*******************************************************************************
 * File Name          : system_ch32x035.c
*******************************************************************************/

#include "ch32x035.h"
#include "global.h"



uint32_t SystemCoreClock;

__I uint8_t AHBPrescTable[16] = {1, 2, 3, 4, 5, 6, 7, 8, 1, 2, 3, 4, 5, 6, 7, 8};



void SetSysClock(uint32_t clock);

static void SetSysClockToX_HSI(uint32_t div, uint8_t latency);


/*********************************************************************
 * @fn      SystemInit
 *
 * @brief   Setup the microcontroller system Initialize the Embedded Flash Interface,
 *        update the SystemCoreClock variable.
 *
 * @return  none
 */
void SystemInit (void)
{
    // ensure internal oscillator is running and ready
    RCC->CTLR  |= (uint32_t)RCC_HSION;
    while (!(RCC->CTLR & RCC_HSIRDY)) {};

    // default to 8MHz before doing anything else
    // this is POR default
    RCC->CFGR0 = (uint32_t)RCC_HPRE_DIV6;

    // set user-requested startup clock
    SetSysClock(SYSCLK_FREQ_STARTUP);
}

/*********************************************************************
 * @fn      SystemCoreClockUpdate
 *
 * @brief   Update SystemCoreClock variable according to Clock Register Values.
 *
 * @return  none
 */
void SystemCoreClockUpdate (void)
{
    uint32_t tmp = 0;

    SystemCoreClock = HSI_VALUE;
    tmp = AHBPrescTable[((RCC->CFGR0 & RCC_HPRE) >> 4)];

    if(((RCC->CFGR0 & RCC_HPRE) >> 4) < 8) {
        SystemCoreClock /= tmp;
    } else {
        SystemCoreClock >>= tmp;
    }
}

/*********************************************************************
 * @fn      SetSysClock
 *
 * @brief   Configures the System clock frequency, HCLK prescalers.
 *
 * @return  none
 */
void SetSysClock(uint32_t clock)
{
    switch (clock) {
        case SYSCLK_FREQ_48MHz_HSI: { SetSysClockToX_HSI(RCC_HPRE_DIV1,  FLASH_ACTLR_LATENCY_2); break; }
        case SYSCLK_FREQ_24MHz_HSI: { SetSysClockToX_HSI(RCC_HPRE_DIV2,  FLASH_ACTLR_LATENCY_1); break; }
        case SYSCLK_FREQ_16MHz_HSI: { SetSysClockToX_HSI(RCC_HPRE_DIV3,  FLASH_ACTLR_LATENCY_1); break; }
        case SYSCLK_FREQ_12MHz_HSI: { SetSysClockToX_HSI(RCC_HPRE_DIV4,  FLASH_ACTLR_LATENCY_0); break; }
        case SYSCLK_FREQ_3MHz_HSI:  { SetSysClockToX_HSI(RCC_HPRE_DIV16, FLASH_ACTLR_LATENCY_0); break; }
        default: {
            SetSysClockToX_HSI(RCC_HPRE_DIV6, FLASH_ACTLR_LATENCY_0);
            clock = 8000000;
            break;
        }
    }

    SystemCoreClock = clock;
}


static void SetSysClockToX_HSI(uint32_t div, uint8_t latency)
{
    uint32_t cfgr0;

    // set flash access to 2 wait states (boot default is 0 at 48MHz??)
    FLASH->ACTLR = (uint32_t)FLASH_ACTLR_LATENCY_2;
    
    // the vendor didn't wait here. but switching from slow to high speed
    // often causes crashes without this.
    asm("nop"); asm("nop"); asm("nop");

    /* HCLK = SYSCLK = APB1 */
    cfgr0 = RCC->CFGR0 &= (uint32_t)~RCC_HPRE;
    RCC->CFGR0 = (uint32_t)(cfgr0 | (div & 0xf0));

    /* Flash set wait state */
    FLASH->ACTLR = (uint32_t)(latency & 0x03);
}